docs: def _get_inter_event_std(self, C, mag, sa1180, vs30):
          """
          Returns inter event (tau) standard deviation (equation 25, page 1046)
          """
          if mag < 5:
              tau_al = C['s3']
          elif mag <= 7:
              tau_al = C['s3'] + (C['s4'] - C['s3']) / 2. * (mag - 5.)
          else:
              tau_al = C['s4']
          tau_b = tau_al
          tau = tau_b * (1 + self._get_derivative(C, sa1180, vs30))
          return tau